ORA-00998: must name this expression with a column alias

问题描述：创建视图时报错ORA-00998，如下所示：
SQL> create view v_emp80
  2   as select employee_id,first_name || ' ' || last_name,salary,department_id
  3        from employees
  4       where department_id=80;

 as select employee_id,first_name || ' ' || last_name,salary,department_id
                                          *
ERROR at line 2:
ORA-00998: must name this expression with a column alias

异常原因：创建视图时，表达式需要别名，才能作为视图的列名，否则会报错.
添加别名后成功创建视图.
SQL> create view v_emp80
  2      as select employee_id,first_name || ' ' || last_name name,salary,department_id
  3           from employees
  4          where department_id=80;

View created.